(1) Field of the Invention
The present invention relates to an aluminum alloy cylinder block. More specifically, the invention relates to a design for minimizing thermal distortion of an aluminum alloy cylinder block for use in an internal combustion engine.
(2) Prior Art
It is known that a reduction in engine weight can be attained most effectively by making an engine cylinder block of aluminum alloy instead of cast iron. If the aluminum alloy cylinder block duplicates the usual structure of a cast iron cylinder block, however, this change in material brings about various unfavorable results because the coefficient of thermal expansion of aluminum is twice as large as that of cast iron.
FIG. 1 is a sectional view of a conventional cast iron cylinder block with a cylinder 2 in which no special structure other than a water jacket 3 surrounding the outer periphery of the cylinder is provided to suppress the thermal deformation of a bore inside of the cylinder.
In particular, an aluminum alloy cylinder block with such a conventional structure will suffer from a large consumption of oil because the expansion of the cylinder bores after warming-up of the engine becomes twice as large as that in the case of the same cylinder block made of cast iron.
Furthermore, the greater the dimensional difference in the cylinder block between cooled and heated states, the more difficult it is to set an appropriate clearance between the bores and pistons to avoid scuffing, seizing or the like.
For the purpose of resolving such drawbacks, there have been proposed an arrangement in which a ring of a low expansion coefficient material is cast into the circumference of the cylinder and an arrangement in which a belting means is wound around the cylinder so as to restrain the deformation of the bore. However, both these arrangements are difficult to manufacture and result in high production costs.